Carbonaceous sulfur hydride system: The strong-coupled room-temperature superconductor with a low value of Ginzburg–Landau parameter

Abstract

The superconducting state in a carbonaceous sulfur hydride (C–S–H) system is probably characterized by the record-high critical temperature of 288 K ([Formula: see text] GPa). We determined the properties of the C–S–H superconducting phase within the scope of both classical Eliashberg equations and the Eliashberg equations with vertex corrections. We took into account the scenarios pertinent to either the intermediate or the high value of an electron–phonon coupling constant ([Formula: see text] or [Formula: see text], respectively). The scenario for the intermediate value, however, cannot be actually realized due to the anomalously high value of the logarithmic phonon frequency ([Formula: see text] K) it would require. On the other hand, we found it possible to reproduce correctly the value of [Formula: see text] and other thermodynamic quantities in the case of strong coupling, with all the reservations discussed in the presented paper. The vertex corrections lower the order parameter values within the range from [Formula: see text]50 K to [Formula: see text]275 K. For the upper critical field [Formula: see text] T, the Ginzburg–Landau parameter [Formula: see text] is of the order of [Formula: see text]. The strong-coupling scenario for the C–S–H system is also suggested by the high values of [Formula: see text] estimated for [Formula: see text] ([Formula: see text], [Formula: see text]), [Formula: see text] ([Formula: see text]–[Formula: see text], [Formula: see text]), and [Formula: see text] ([Formula: see text], [Formula: see text]) compounds. In the case of the C–S–H system, we also anticipate the presence of the antiferromagnetic state above the superconducting state like in the dense [Formula: see text] superconductor. For [Formula: see text] GPa and [Formula: see text] K, the magnetic ordering transition occurs at [Formula: see text] K.